PHNOM PENH: Cambodian Prime Minister Hun Sen on Thursday lashed out at a UN human rights envoy for writing "untrue" reports about the Southeast Asian nation, saying he should worry about his homeland Nepal instead.

The attack follows a scathing report by Surya Subedi last month that said a series of Cambodian land disputes "indicate an increasingly desperate and unhappy population".

While Hun Sen did not accuse Subedi by name, the strongman premier said the author of the "untrue" writings was a national of a country that "has already abolished the monarchy" and "at this hour... has no constitution".

"Hopefully, he will go and help his own country. That would be better than helping Cambodia," Hun Sen said in a speech to graduating students in Phnom Penh.

Subedi was born in Nepal, where the monarchy was abolished in 2008. The nation's parliament was dissolved earlier this year after politicians failed to draw up a constitution by an agreed deadline.

Hun Sen's remarks appear to be the strongest yet against the Oxford-educated law professor, who became UN special rapporteur for human rights in Cambodia in 2009 after his predecessor resigned amid a war of words with Phnom Penh.

Hun Sen, who has been in power since 1985 and is seeking re-election next year, also took a swipe at the UN human rights office in Cambodia, reminding its staff they were merely "long-term tourists" and he could refuse to work with them at any time.

"If you don't work appropriately, I will not meet with you," he said.

Activists say land conflicts are Cambodia's most pressing human rights issue. Protests have intensified this year and campaigners say the authorities are increasingly cracking down on dissent.